You can also check out the Ham Academy at
AH0A. Look at his study notes and take the practice tests.
There are 3 levels of amateur radio operator in the United States today: Technician, General, and Extra.
As a Technician, you can work local repeaters and any communication mode on 50 MHz and up. A General has privileges on HF: the frequencies below 50 MHz, but with some limitations. An extra has all the HF bands open to him.
The only real difference between General and Extra is a few KHz of bandwidth on some of the more popular bands.
You will want to start by studying for the Technician class: this gets you in to local repeaters. If you want to expand in to trying to work DX (long-range contacts), you can then study for your General. But before you do that, find a club and get to know some guys; see if a General or Extra will let you sit in with them and work the bands. If you think you'd enjoy it, then you can work on that license class.
You can also study with a test guide, like
Ham Radio for Dummies (I'm not kidding... I bought & studied with that book) and just take a test at a local testing site. Also, look for a Ham Radio Outlet nearby; the guys there are usually very helpful. After all, if you pass, you'll be their customer.
The ARRL isn't the best place to find out about Ham classes tests in your area, mostly because it doesn't list all the test sessions. Here in San Diego, I tried to view the ARRL list of tests, and it left out nearly all of the tests and classes administered by the local amateur groups. Rather than use their test list, use their list of clubs to find a local club or use Google to find local clubs. Find the nearest club, call the telephone number on the web site, and talk to the guy who answers. He'll be able to help you find a class and testing site.
The actual test is pretty straightforward: there are 35 questions, multiple choice, and they'll relate to a few categories: radio safety, operation, some regulations, and probably knowing something about band limits.